1. Field of the Invention
The present invention relates to optical SNR boosters. More particularly, the present invention relates to nonlinear optical loop mirrors unbalanced by one or more nonlinearities.
2. Description of Related Art
As the number of wavelengths in wavelength-division multiplexed (WDM) systems increases, electronic regenerators can increasingly dominate the cost of transmission links. One electronic regenerator can be required per wavelength channel, and for N wavelengths the cost of the N regenerators can become prohibitive. N can presently approach 100 or larger. An electronic regenerator can be a so-called 3-R regenerator, restoring timing, pulse shape, and pulse amplitude. Optical amplifiers have been a key enabler for WDM networks because a single amplifier can simultaneously provide gain to a number of wavelength channels. By using an all-optical solution, the transmission line can be at least semi-transparent by avoiding optical-to-electronic and electronic-to-optical conversions.
A typical fiber-optic transmission line can have periodically-spaced optical amplifiers to compensate for the loss of the fiber. Each amplifier, however, can introduce noise, or amplified spontaneous emission, during the amplification process, which in turn can degrade the SNR. As the signal traverses more amplifiers, the SNR can decrease. In a telecommunication system, an electronic regenerator can be typically inserted every five amplifier spans, corresponding to about 400-600 km between regenerators (c.f. FIG. 1). The optical amplifier can be a 1-R device restoring signal amplitude, while the regenerator can boost the SNR and perform the 3-R functions. As the number of wavelengths increases and the cost of amplifiers decreases, the economics of the transmission links can be dominated by the regenerators. In addition, the physical size or footprint of these electronic regenerators in a central office begins to dominate the cost.
To increase the capacity of systems while reducing the cost, several upgrades can be being planned. First, the amplifier span can be increased. Second, the bit-rate per channel can be increased. Third, more channels of WDM at new wavelengths can be added. All three of these steps can lead to a degradation of the SNR. To permit these upgrades while reducing the need for electronic regeneration, the SNR can be periodically boosted. In WDM systems the SNR booster can be used with multiple wavelength channels without increasing cost or complexity along with the number of channels.
The 3R functionality can be difficult to achieve all-optically for multiple wavelengths. Restoration of amplitude can be achieved using an amplifier, and reshaping can be done using pulse reshaping in solitons. Re-timing can be difficult to accomplish except on a channel-by-channel basis such as with an electronic regenerator. For operation at multiple wavelengths, the timing between channels can vary since each wavelength can have a different group velocity dispersion. Timing extraction or clock recovery for multiple wavelength channels can be done with physically separated channels. In all-optical solutions re-timing can be difficult with a fixed speed-of-light. Building an all-optical 3-R regenerator can be difficult.
One step toward an all-optical regenerator can be an all-optical signal-to-noise ratio (SNR) booster, or optical sweeper. Therefore, what is needed is an optical SNR booster that can simultaneously operate for multiple wavelength channels and/or can remove both in-band and out-of-band noise.
The all-optical SNR booster can remove in-band and out-of-band noise. The all-optical SNR booster can simultaneously operate for multiple wavelength channels. The SNR booster can permit an increase in the spacing between electronic regenerators, thereby reducing the cost of the system.
The optical sweeper can reduce the cost of systems and permit bandwidth upgrades. The optical sweeper can have applications in long-haul, metro and router networks, and can apply to new and legacy systems. The optical sweeper can reconfigure current optical amplifiers to simultaneously amplify, dispersion compensate, and boost the signal to noise ratio. One optical sweeper embodiment can be an all-fiber embodiment made from commercially available parts.
One embodiment of a non-linear optical loop mirror for processing optical signals can include an optical fiber, a bi-directional amplifier, and a coupler. The optical fiber can include a signal input and a signal output. At least a portion of the optical fiber can include a dispersion compensating fiber. At least a portion of the optical fiber can form a loop. The dispersion compensating fiber can have an absolute magnitude of dispersion of at least 20 ps/nm-km for at least a portion of wavelengths in the optical signals. The bi-directional amplifier can be coupled to the optical fiber. The coupler can be coupled to a first portion of the optical fiber and a second portion of the optical fiber to form a fiber loop.
One embodiment of a non-linear optical loop mirror for processing optical signals can include a first optical fiber, a second optical fiber, a bi-directional amplifier, and a coupler. The first optical fiber can include a signal input and a signal output. The second optical fiber can be coupled to the first optical fiber to form a fiber loop. At least a portion of the second optical fiber can include a dispersion compensating fiber that can have an absolute magnitude of dispersion of at least 20 ps/nm-km for at least a portion of wavelengths in the optical signals. The bi-directional amplifier can be coupled to at least one of the first and second optical fibers. The coupler can be coupled to the first and second optical fibers.
One embodiment of a method of processing optical signals can include providing a non-linear optical loop mirror that includes a dispersion compensating fiber and a fiber loop, the dispersion compensating fiber having an absolute magnitude of dispersion of at least 20 ps/nm-km for at least a portion of wavelengths in the optical signals; introducing the optical signal to the non-linear optical loop mirror; and simultaneously amplifying and dispersion compensating the optical signal in the non-linear optical loop mirror.
One embodiment of a non-linear optical loop mirror for processing optical signals can include an optical fiber, a bi-directional amplifier, and a coupler. The optical fiber can include a signal input, a signal output, and a fiber loop. At least a portion of the optical fiber can include a sufficiently large dispersion to minimize phase shift interactions between adjacent wavelength signals of the optical signals. At least a portion of the optical fiber can form a fiber loop. The bi-directional amplifier can be coupled to the optical fiber. The coupler can be coupled to the fiber loop.
One embodiment of an optical regeneration system can include a wavelength demultiplexer, a wavelength multiplexer, and a plurality of nonlinear optical loop mirrors. Each of the plurality of nonlinear optical loop mirrors can include a first fiber, a second fiber, a coupler, and a first optical amplifier. The first fiber can include a first end, a second end, and a first effective nonlinearity. The first effective nonlinearity can be determined at least by an index of refraction of the first fiber and an effective area of the first fiber. The second fiber can include a first end, a second end, and a second effective nonlinearity determined at least by an index of refraction of the second fiber and an effective area of the second fiber. The first effective nonlinearity can be distinct from the second effective nonlinearity. The coupler can be coupled to the first end of the first fiber, the first end of the second fiber, the wavelength demultiplexer, and the wavelength multiplexer. The first optical amplifier can be coupled to the second end of the first fiber and the second end of the second fiber. The first optical amplifier amplifies at least signals traveling in a first direction from the second end of the first fiber to the second end of the second fiber and signals traveling in a second direction from the second end of the second fiber to the second end of the first fiber.
One embodiment of an optical system for processing optical signal, can include an input optical fiber, a splitter, and at least a first loop mirror. The splitter can be coupled to the input optical fiber. The splitter separates adjacent channels of an input optical signal. At least a first loop mirror can be coupled to the splitter. At least a first loop mirror includes a fiber loop. At least a portion of the fiber loop includes a dispersion compensating fiber. At least a portion of the dispersion compensating fiber can have an absolute magnitude of dispersion of 20 ps/nm-km for a majority of wavelengths in the optical signals.
One embodiment of a non-linear optical loop mirror can include a first optical fiber, a second optical fiber, and a coupler. The first optical fiber can include a first effective non-linearity. The second optical fiber can be coupled to the first optical fiber and can form a fiber loop. The second optical fiber can include a second effective non-linearity that can be different from the first effective non-linearity. The coupler can be coupled to the first and second optical fibers. A length of the first optical fiber can be greater than a walk-off length for at least a portion of adjacent wavelengths propagating in the first fiber.
One embodiment of a non-linear optical loop mirror can include a first optical fiber, a second optical fiber, bi-directional amplifier, and a coupler. The first optical fiber can include a first effective non-linearity. The second optical fiber can be coupled to the first optical fiber and can form a fiber loop. The second optical fiber can include a second effective non-linearity that can be different from the first effective non-linearity. The bi-directional amplifier can be coupled to at least one of the first and second optical fibers. The coupler can be coupled to the first and second optical fibers.